1. Field of the Invention
The present invention relates to a light source device for an endoscope and an endoscope system.
2. Description Related to the Prior Art
In medical fields, diagnoses using endoscope systems are widely performed. The endoscope system comprises a light source device for an endoscope (hereinafter simply referred to as the light source device), an endoscope, and a processor device. The light source device generates illumination light with which an object of interest (hereinafter simply referred to as the object, e.g. mucosa or the like in a body cavity) is to be irradiated. The endoscope system is provided with a normal mode and an oxygen saturation mode. In the normal mode, normal observation using normal illumination light (white light) is performed. In the oxygen saturation mode, various types of observation using special illumination light are performed. The observation of oxygen saturation levels (hereinafter referred to as the oxygen saturation observation) is one of them.
The oxygen saturation observation is a method of observation in which oxygen saturation levels that indicate how much oxygen is contained in blood in blood vessels are calculated and an image representing the oxygen saturation levels is displayed. The oxygen saturation observation is performed by using light (measurement light) whose wavelength range is limited to 450 to 500 nm, in which a difference between the absorption coefficient of oxyhemoglobin and the absorption coefficient of deoxyhemoglobin (in blood vessels) is large (see US2012/0157768 (corresponding to Japanese Pat. No. 5303012)).
In the normal observation, the reduction in contrast (hereinafter referred to as the blood vessel contrast) between the mucosal surface and the blood vessels is prevented by reducing the intensity of a light component in the wavelength range of 460 to 500 nm of normal light (white light) (see US2011/0288387 (corresponding to Japanese Pat. No. 5306447)). This is based on the fact that a difference in reflectance between the blood vessel and the mucosa surrounding the blood vessel is small in the wavelength range greater than or equal to 460 nm. Thereby, the blood vessel contrast in the image is increased.
A broadband light source such as a xenon lamp, a white LED (Light Emitting Diode), or the like is used as the light source device. Recently, a combination of semiconductor light sources of different colors (e.g. a blue LED, a green LED, and a red LED) has been used. With regard to a blue light source, a blue LED having a peak wavelength around 450 to 460 nm is used.
As described in the US2012/0157768 and the US2011/0288387, the illumination light having the wavelength range of 450 to 500 nm is used for the oxygen saturation observation. With regard to the illumination light for the normal observation using an image in which the blood vessel contrast is increased, the intensity of the illumination light in the wavelength range of 460 to 500 nm is reduced. In other words, the blue illumination light for the normal observation differs in wavelength from that for the oxygen saturation observation. For this reason, it is necessary to use different light sources for the normal observation and the oxygen saturation observation, respectively. The two types of observation cannot be performed by using a single endoscope system.